This invention relates to a miniature pressure sensor using a fiber optic element for use where the pressure sensor must be very small. Such a sensor may be particularly adapted for combustion pressure measurements in a combustion chamber of an internal combustion engine by inclusion within a spark plug. It must be small and sufficiently rugged to withstand the high temperatures and pressures in a combustion environment; but it must be inexpensive to manufacture if mass production is contemplated.
A sensor well adapted for such use may be micromachined in silicon for operational ruggedness and low expense in large quantities. Its operation is based on the variation of proximity coupling between an optic fiber and a surface wave on a pressure sensitive membrane; and the structure can thus be much smaller than, for example, an optic fiber sensor of the microbend type. However, the small size of the sensor and the small scale of the pressure responsive deflections of the membrane subject such a sensor to temperature variations in output due to the temperature responsive expansion and contraction of silicon and similar materials.